Network Rail has completed the £40 million upgrade of stabling sidings at Cricklewood.
The facility is used by Govia Thameslink Railway, and will host the Siemens Class 700 electric multiple units when they are introduced from the spring.
Able to accommodate 22 trains, it was built by Carillion on disused sidings near to the existing depot. A carriage wash, toilet emptying facilities and walkways for staff to remove rubbish from trains have been provided.
There are five 600-metre and three 300-metre sidings, which can accommodate ten 12-car trains at the southern end and 12 eight-car trains at the northern end.